This Invention relates to a filler metal for use in the welding of Nixe2x80x94Crxe2x80x94W alloys that are excellent in high-temperature strength and corrosion resistance and which are used in the hot-zone structures of high-temperature gas-cooled reactors, gas turbines, etc.
Heretofore, Nixe2x80x94Crxe2x80x94W and Nixe2x80x94Crxe2x80x94Wxe2x80x94Mo alloys have been developed as super-heat resistant materials for use in the hot-zone structures of high-temperature gas-cooled reactors, gas turbines, etc. These alloys are used at high temperatures near 1000xc2x0 C. and required to be excellent in high-temperature creep strength and corrosion resistance.
To meet these requirements, Nixe2x80x94Cr alloys strengthened with W or Mo have been proposed in Japanese Patent Public Disclosure Nos. 29316/1976, as well as Japanese Patent Publication Nos. 33212/1979 and 47612/1993. Welding is employed to fabricate structures with these alloys. Since the fabricated structures are put to prolonged service at high temperatures, the welded portions must also have high-temperature creep strength.
Japanese Patent Public Disclosure No. 29316/1976 teaches a heat-resistant alloy for use in the fabrication of welded structures with Nixe2x80x94Crxe2x80x94W and Nixe2x80x94Crxe2x80x94Wxe2x80x94Mo alloys but the patent is limited to a compositional range of 3-20% W alloys that indicates low susceptibility to cracking in weldments. Nixe2x80x94Crxe2x80x94W alloys are so sensitive to weld cracking that if an alloy having an identical chemical composition to the base metal is used as a filler metal, weld cracking occurs, making it difficult to fabricate sound welded structures. In order to assure integrity of high-temperature structures, the welded portions must have a high-temperature creep strength comparable to that of the base metal. In the case of Nixe2x80x94Crxe2x80x94W alloys, no filler metal has yet been developed that can be worked Into a welding wire, that has good weldability and that produces welded portions having comparable high-temperature creep strength to the base metal.
An object, therefore, of the present invention is to provide a welding filler metal suitable for use with Nixe2x80x94Crxe2x80x94W alloys which have originally high susceptibility to cracking in weldments. The welding filler metal has enough hot workability Into a welding wire, excellent weldability and capability which produces welded portions having comparable high-temperature creep strength to the base metal.
This object of the invention can be attained by a filler metal for use in the welding of Nixe2x80x94Crxe2x80x94W alloys which comprises on a mass basis:
Cxe2x89xa60.05%
Mnxe2x89xa60.1%
Sixe2x89xa60.1% (Mn+Sixe2x89xa60.1%)
Cr=17-20%
W=20-23% (Cr+W=39-43%)
Ti=0.02-0.1%
Zrxe2x89xa60.03%
Yxe2x89xa60.015%
B=0.0003-0.01%
Alxe2x89xa60.1%
Mgxe2x89xa60.05%
Nbxe2x89xa60.06% (10Zr+10B+5Nb+2Yxe2x89xa60.3%)
the balance being Ni and incidental impurities.